Patent GB-797193-A (GB)
Title: Improvements in the manufacture of artificial filamentary materials
Inventor: GROOMBRIDGE DENIS WILLIAM
IPC: D01F2/28
Filed: 1955-07-11
Abstract: <PICT:0797193/IV (a)/1> Cellulose triacetate filaments and like products are made by extruding a solution of cellulose triacetate into a coagulating bath, drawing the products so produced through the bath at a draw-down ratio below 1.5, preferably below 1.25, and subsequently drying the products while they are allowed to shrink freely or by at least 75 per cent of the amount by which they would shrink if allowed to shrink freely.  Before being dried the products are usually washed free from adherent coagulant or the latter, if volatile, may be removed by evaporation in the drying operation. The spinning solvent is preferably acetic acid, and the spinning solution may be obtained by acetylating cellulose in the presence of sulphuric acid as catalyst and of acetic acid to dissolve the cellulose triacetate formed, "ripening" the solution to reduce the combined sulphate content of the product, neutralizing the catalyst and diluting the solution to the required viscosity.  The spinning solvent may also be a mixture of methylene or ethylene chloride with about 5-12 per cent of methanol or ethanol.  When acetic acid is the solvent the coagulant is preferably water or aqueous acetic acid of concentration below about 55 per cent by weight, acetic acid of 10-25 per cent concentration being suitable.  It may contain a salt such as an alkali-metal acetate. When the solvent is a mixture of methylene or ethylene chloride with an alcohol, the coagulant is preferably an alcohol, particularly the same as is present in the spinning solution.  The alcohol used as coagulant may contain up to 20 per cent by weight or more of water and is preferably cooled to below room temperature, e.g. to +10 DEG  C. to -10 DEG  C. or lower, and also caused to flow through the spinning zone sufficiently rapidly to keep its content of methylene or ethylene chloride below 6 per cent by weight.  The draw-down ratio employed is preferably below 1.1 and may be unity or below.  After leaving the bath, the products may be passed over a stripping device to remove adherent liquid, e.g. a series of bars between which the material follows a zig-zag path, or a free-running roller as described in Specification 787,563.  A liquid freely miscible with the coagulant, and substantially without solvent or swelling action for cellulose triacetate, such as used washing liquid, may be applied to the products shortly before or as they leave the stripping device, as described in Specification 797,194, especially when a yarn or tow containing a large number of filaments is being made.  As shown, a neutralized and diluted acetylation solution of cellulose triacetate (14.3 per cent) in acetic acid is fed through the dope feed line 3 to the spinning jet 2 through which it is extruded into 18 per cent aqueous acetic acid in the spinning vessel 1. The aqueous acid is fed into the vessel 1 through the inlets 4 and packing 5 and overflows at the top into the gutter 6, which it leaves by the run-off 7.  The filaments 5 so produced converge to form a tow 25 which is passed in a zig-zag path between the off-set parallel smooth bars 8 by means of the godet 9 and associated skew idler roller 10.  From the godet 9 the tow is passed to a washing device comprising the skewed rollers 11, 12, the latter being at a small angle to the horizontal.  The tow is washed with water from the spray nozzle 13 until its acetic acid content (based on its dry weight) does not exceed 3 per cent.  The waste wash liquors are collected in the trough 14 from which the bulk is discharged through the constant-level run-off 15, a small proportion being pumped by means of the pump 17 through the line 16 to the nozzle 18 and so directed on to the tow as it passes round the last of the bars 8.  The tow then passes to a drying device comprising a pair of steam-heated rolls 19, 20 set skew with respect to each other and so tapered as to allow the tow to shrink by 18-20 per cent of its length, this being the degree of shrinkage found to occur when the tow is dried free from tension. The dried tow passes over a godet 21 of the type described in Specification 787,555, [Group IX], and is collected in the sliver can 24.  Filaments produced as described above have a high extension at break.